Unpaired 3d Electrons Research Articles

The Role of Rare-Earth Atoms in the Anisotropy and Antiferromagnetic Exchange Coupling at a Hybrid Metal-Organic Interface.

Magnetic anisotropy and magnetic exchange interactions are crucial parameters that characterize the hybrid metal-organic interface, a key component of an organic spintronic device. It is shown that the incorporation of 4f RE atoms to hybrid metal-organic interfaces of CuPc/REAu2 type (RE = Gd, Ho) constitutes a feasible approach toward on-demand magnetic properties and functionalities. The GdAu2 and HoAu2 substrates differ in their magnetic anisotropy behavior. Remarkably, the HoAu2 surface promotes the inherent out-of-plane anisotropy of CuPc, owing to the match between the anisotropy axis of substrate and molecule. Furthermore, the presence of RE atoms leads to a spontaneous antiferromagnetic exchange coupling at the interface, induced by the 3d-4f superexchange interaction between the unpaired 3d electron of CuPc and the 4f electrons of the RE atoms. It is shown that 4f RE atoms with unquenched quantum orbital momentum ( ), as it is the case of Ho, induce an anisotropic interfacial exchangecoupling.

Electrodeposition of Ni/Cu Bimetallic Conductive Metal-Organic Frameworks Electrocatalysts with Boosted Oxygen Reduction Activity for Zinc-Air Batteries.

Zinc-air batteries employing non-Pt cathodes hold significant promise for advancing cathodic oxygen reduction reaction (ORR). However, poor intrinsic electrical conductivity and aggregation tendency hinder the application of metal-organic frameworks (MOFs) as active ORR cathodes. Conductive MOFs possess various atomically dispersed metal centers and well-aligned inherent topologies, eliminating the additional carbonization processes for achieving high conductivity. Here, a novel room-temperature electrochemical cathodic electrodeposition method is introduced for fabricating uniform and continuous layered 2D bimetallic conductive MOF films cathodes without polymeric binders, employing the organic ligand 2,3,6,7,10,11-hexaiminotriphenylene (HITP) and varying the Ni/Cu ratio. The influence of metal centers on modulating the ORR performance is investigated by density functional theory (DFT), demonstrating the performance of bimetallic conductive MOFs can be effectively tuned by the unpaired 3d electrons and the Jahn-Teller effect in the doped Cu. The resulting bimetallic Ni2.1Cu0.9(HITP)2 exhibits superior ORR performance, boasting a high onset potential of 0.93V. Moreover, the assembled aqueous zinc-air battery demonstrates high specific capacity of 706.2mA h g-1, and exceptional long-term charge/discharge stability exceeding 1250 cycles.

Microwave-assisted exploration of the electron configuration-dependent electrocatalytic urea oxidation activity of 2D porous NiCo2O4 spinel

Urea holds promise as an alternative water-oxidation substrate in electrolytic cells. High-valence nickel-based spinel, especially after heteroatom doping, excels in urea oxidation reactions (UOR). However, traditional spinel synthesis methods with prolonged high-temperature reactions lack kinetic precision, hindering the balance between controlled doping and highly active two-dimensional (2D) porous structures design. This significantly impedes the identification of electron configuration-dependent active sites in doped 2D nickel-based spinels. Herein, we present a microwave shock method for the preparation of 2D porous NiCo2O4 spinel. Utilizing the transient on-off property of microwave pulses for precise heteroatom doping and 2D porous structural design, non-metal doping (boron, phosphorus, and sulfur) with distinct extranuclear electron disparities serves as straightforward examples for investigation. Precise tuning of lattice parameter reveals the impact of covalent bond strength on NiCo2O4 structural stability. The introduced defect levels induce unpaired d-electrons in transition metals, enhancing the adsorption of electron-donating amino groups in urea molecules. Simultaneously, Bode plots confirm the impact mechanism of rapid electron migration caused by reduced band gaps on UOR activity. The prepared phosphorus-doped 2D porous NiCo2O4, with optimal electron configuration control, outperforms most reported spinels. This controlled modification strategy advances understanding theoretical structure-activity mechanisms of high-performance 2D spinels in UOR.

Unraveling the role of unpaired 3d electrons in eg orbital of CoO: Driving π feedback of N2 for efficient ammonia electrosynthesis

Transition metal oxides (TMOs) have been emerged as efficient electrocatalysts for ammonia (NH3) electrosynthesis. However, the relationship between the d electron configuration of TMOs and their catalytical activity needs to be deeply understood towards for electrochemical nitrogen reduction reaction (ENRR). Herein, we focused on illustrating the effect of orbital occupation/distribution of d electrons on the ENRR performance of Cobalt oxides by deliberately selecting CoO (with a t2g5eg2 electron configuration of Co2+) and Co2O3 (with a t2g6eg0 electron configuration of Co3+) as modeling catalysts. Interestingly, the CoO catalyst exhibited a high ammonia yield of 33.46 μg h−1 mgcat−1 at −0.6 V versus reversible hydrogen electrode (RHE) and a prominent faradic efficiency (FE) of 5.1%, which apparently outperforms the Co2O3 catalyst. We used XAS, M-T and MFM to thoroughly characterize the electronic structure of the active center of the samples. Importantly, Theoretical calculations and In-situ techniques demonstrated that the unpaired electrons in eg orbital of Co2+ play crucial role in boosting the adsorption and activation of N2 on CoO. In specific, the t2g5eg2 electron configuration delivers more electron from Co2+ to N2 and the unpaired electrons in eg orbital of Co2+ site promote surprisingly the π-feedback process from CoO to N2, resulting a lower hydrogenation energy barrier for N2 activation. This work provides a deep understanding of the structure–function relationship of TMOs catalyst for ENRR.

Long-range electron synergy over Pt1-Co1/CN bimetallic single-atom catalyst in enhancing charge separation for photocatalytic hydrogen production

The development of novel single-atom catalysts with optimal electron configuration and economical noble-metal cocatalyst for efficient photocatalytic hydrogen production is of great importance, but still challenging. Herein, we fabricate Pt and Co single-atom sites successively on polymeric carbon nitride (CN). In this Pt1-Co1/CN bimetallic single-atom catalyst, the noble-metal active sites are maximized, and the single-atomic Co1N4 sites are tuned to Co1N3 sites by photogenerated electrons arising from the introduced single-atomic Pt1N4 sites. Mechanism studies and density functional theory (DFT) calculations reveal that the 3d orbitals of Co1N3 single sites are filled with unpaired d-electrons, which lead to the improved visible-light response, carrier separation and charge migration for CN photocatalysts. Thereafter, the protons adsorption and activation are promoted. Taking this advantage of long-range electron synergy in bimetallic single atomic sites, the photocatalytic hydrogen evolution activity over Pt1-Co1/CN achieves 915.8 mmol·g-1Pt·h−1, which is 19.8 times higher than Co1/CN and 3.5 times higher to Pt1/CN. While this electron-synergistic effect is not so efficient for Pt nanoclusters. These results demonstrate the synergistic effect at electron-level and provide electron-level guidance for the design of efficient photocatalysts.

Photoelectron Spectroscopy and Theoretical Studies of Ge6MnO- Cluster with a MnV≡O Unit Interacting with a Double Aromatic Ge64- Ligand.

The structures and chemical bonding of Ge6MnO- are investigated using anion photoelectron spectroscopy and theoretical calculations. The lowest energy structure of Ge6MnO- is found to have a C5v symmetric structure with an O atom attached to a pentagonal bipyramidal MnGe6. Chemical bonding analyses reveal that Ge6MnO- can be considered as a [MnV≡O]3+[Ge64-] complex with two unpaired 3d electrons on Mn. The Ge64- ligand is highly stable in Ge6MnO- and exhibits double aromaticity with 10 delocalized σ electrons and 6 delocalized π electrons. Our calculations show that the Ge64- ligand could also form [CrIV≡O]2+[Ge64-] in Na2Ge6CrO and [FeIV≡O]2+[Ge64-] in Na2Ge6FeO. The results suggest the possibility of designing and synthesizing a series of stable high-valent metal oxide anionic species with the composition [M≡O]n+[Ge64-] in the gas phase or in the salt-stabilized bulk solid materials.

Isolating Fe-O2 Intermediates in Dioxygen Activation by Iron Porphyrin Complexes.

Dioxygen (O2) is an environmentally benign and abundant oxidant whose utilization is of great interest in the design of bioinspired synthetic catalytic oxidation systems to reduce energy consumption. However, it is unfortunate that utilization of O2 is a significant challenge because of the thermodynamic stability of O2 in its triplet ground state. Nevertheless, nature is able to overcome the spin state barrier using enzymes, which contain transition metals with unpaired d-electrons facilitating the activation of O2 by metal coordination. This inspires bioinorganic chemists to synthesize biomimetic small-molecule iron porphyrin complexes to carry out the O2 activation, wherein Fe-O2 species have been implicated as the key reactive intermediates. In recent years, a number of Fe-O2 intermediates have been synthesized by activating O2 at iron centers supported on porphyrin ligands. In this review, we focus on a few examples of these advances with emphasis in each case on the particular design of iron porphyrin complexes and particular reaction environments to stabilize and isolate metal-O2 intermediates in dioxygen activation, which will provide clues to elucidate structures of reactive intermediates and mechanistic insights in biological processes.

Transition-metal single atom catalyst embedded in C2N for toxic-gas reduction reaction and selective gas-sensing application: Atomic-scale study

Exploring advanced materials for detecting noxious gases is a key requirement for maintaining healthy air quality in the environment. The catalytic activity of four magnetic transition metal “TM” elements (e.g., Mn, Fe, Co and Ni) embedded in C2N pores, as single-atom catalysts (SAC), has been tested towards detecting toxic oxidizing gases. As a model, we tested the sensing efficiency of these catalysts towards two toxic gases, namely NO and NO2. For our calculations, we have used a formalism based on the combination of density functional theory (DFT) and non-equilibrium green’s function (NEGF). From our findings we have drawn a strong correlation between the sensor response and the reduction in magnetization (ΔM ≅ −1.40 to −0.55 μB). The results of spin-polarized transport properties showed that Ni- and Fe-embedded C2N are the most efficient in detecting NO/ NO2 and NO2 molecules (with ΔM/M0 = −98%, −38% to −18%, respectively). The main reason for the magnetization reduction was the formation of chemical bonds between SAC and molecules thereby causing an enormous reduction in the number of unpaired d-electrons. Thus, Fe- and Ni-C2N are recommended for either toxic-gas reduction reactions or platform materials in disposable gas sensors for efficient capturing of toxic gases.

A novel tool wear suppression method for polycrystalline diamond by applying magnetic field in turning of ferrous materials

Ferrous materials are widely used in the mould industry because of their excellent properties. However, ferrous materials are regarded as difficult-to-cut materials for diamond turning due to their affinity for diamond. The resulting catastrophic tool wear leads to high machining costs in ultraprecision turning. The unpaired d-electrons in the workpiece are regarded as the dominant element causing catastrophic diamond wear during the turning. However, an insightful method for unpaired d-electrons in existing assisted machining schemes is still lacking. As a type of diamond tool, polycrystalline diamond (PCD) tools are inexpensive to appropriately carry out wear experiments. Therefore, in this study, a novel assisted method based on a magnetic field (MF) was applied to suppress the PCD tool wear. Experimental results demonstrated that the MF-assisted machining can reduce the flank wear of PCD tools by 30.6%. The spin polarisation of d-electrons by the MF was the dominant mechanism inhibiting the chemical reaction and graphitisation, and thus suppressing the PCD tool wear. Simultaneously, the suppression of machining system vibration by the Lorentz force also had a positive effect on the suppression of the PCD tool wear. The innovative method provides an assisted machining scheme to inhibit the catastrophic wear of PCD tools.

DFT investigation of Au9M2+ nanoclusters (M = Sc-Ni): The magnetic superatomic behavior of Au9Cr2+

Au102+ has been found very stable showing a superatomic behavior with a highly symmetrical geometry and can be considered as the smallest copy of the golden pyramid Au20. In this work, we further explore superatomic clusters as analogues of more complex molecules by doping Au102+ cluster with 3d transition metal atom. It is found that, in similarity to their sister Au19M, the structural evolution of Au9M2+ is ruled by the bond strength of AuM dimers and can be generalized into two motifs: the endohedrally doped cage-like structure for lighter dopants (M = Sc and Ti) and the slightly distorted tetrahedral structure for heavier ones. The average binding energies and dissociation energies are calculated to identify the relatively stable patterns. The molecular orbital (MO) diagram as well as the spin distribution are computed to understand the electronic structure and magnetic behavior of studied clusters. The spin magnetic moments of Au9M2+ clusters systematically vary from 0 to 5 μB, depending on the localization of unpaired 3d electrons. With a large spin magnetic moment of 5 μB, the exceptionally stable Au9Cr2+ is identified as a potential magnetic superatom and would be beneficial for further theoretical and experimental studies.

Magnetic Ni doping induced high power factor of Cu2GeSe3-based bulk materials

Cu2GeSe3 is an eco-friendly material, but pristine Cu2GeSe3 has poor thermoelectric properties. Here, the effects of magnetic Ni ion with unpaired 3d electrons on the electrical and thermal transport properties of Cu2GeSe3 are reported. Density functional theory (DFT) calculations indicate that the unpaired Ni 3d states cause the hybridization of Ni 3d orbitals with Se 4p orbitals near the Fermi level, giving rise to an increase in density of states (DOS). Combined with the significantly increased carrier concentration, a power factor (S2σ) value of ∼8.0 μWcm−1 K−2 at 723 K is achieved in Cu2Ge0.8Ni0.2Se3 sample, seeming to be the highest compared with the other Cu2GeSe3 systems. Meanwhile, the substitution of Ni for Ge causes the obvious local distortions in Cu2GeSe3 lattice, which yields the large strain fluctuations to suppress the lattice thermal conductivity. Consequently, a peak ZT value of ∼0.38 at 723 K is obtained in Cu2Ge0.9Ni0.1Se3 sample.

One Responsive Stone, Three Birds: Mn(III)-Hemoporfin Frameworks with Glutathione-Enhanced Degradation, MRI, and Sonodynamic Therapy.

Ultrasound-driven sonodynamic therapy (SDT) catches numerous attentions for destroying deep-seated tumors, but its applications suffer from unsatisfactory therapeutic effects and metabolism. Furthermore, SDT is usually weakened by the complex tumor microenvironment, such as the overexpression of glutathione (GSH). To address these issues, Mn(III)-hemoporfin frameworks (Mn(III)-HFs) are reported as nanosonosensitizers by using biocompatible hematoporphyrin monomethyl-ether (HMME) to coordinate with Mn(III) ions. Mn(III)-HFs/PEG can react with GSH to produce Mn(II) ions and oxidized glutathione (GSSG), resulting in three fascinating features: 1) the redox reaction facilitates the decomposition of Mn(III)-HFs/PEG and then collapse of nanostructures, improving the biodegradability; 2) Mn(II) ions with five unpaired 3d-electrons exhibit better magnetic resonance imaging (MRI) ability compared to Mn(III) ions with four electrons; 3) both the depletion of endogenous GSH and the dissociated HMME boost 1 O2 generation ability under US irradiation. As a result, when Mn(III)-HFs/PEG dispersion is intravenously administered into mice, it exhibits high-contrast T1 /T2 dual-modal MRI and significant suppression for the growth rate of the deep-seated tumor. Furthermore, Mn(III)-HFs/PEG can be efficiently metabolized from the mice. Therefore, Mn(III)-HFs/PEG exhibit GSH-enhanced degradation, MRI, and SDT effects, which provide some insights on the developments of other responsive nanosonosensitizers.

Mesoscopic orbital paramagnetism: The role of zero-point energy

A model is presented to explain the temperature-independent saturating paramagnetic response of some transparent oxides with no unpaired d-electrons. It is based on an array of N surface defect-related electrons with bound states in the gap that can form a coherent mesoscopic many-electron state in response to fluctuations of the zero-point electromagnetic field. Individual electronic orbits expand by 0.083 pm, as in the theory of the Lamb shift, and these expansions add to produce a global volume change. This modifies the energy density in the zero-point electromagnetic field, thereby lowering the energy per electron sufficiently to stabilize a coherent multi-electron state of the two-dimensional system at room temperature. A net magnetic moment can be induced by an applied magnetic field, which mixes coherent ground and excited states, producing a paramagnetic orbital magnetization of magnitude M=MSx1+x2, where x is proportional to the applied field. Orbital saturation moments per coherent surface electron range from 10-3 to 10-1 Bohr magnetons.

A computational study of isoprene polymerization catalyzed by iminopyridine-supported iron complexes: Ligand-controlled selectivity

DFT calculations have been conducted for investigating the relation between the electronic states and catalytic properties of iminopyridine-ligated cationic iron complexes in the stereoselective polymerization of isoprene. Iminopyridine ligand is found to be redox-inert in this catalytic system. The neutral pre-catalyst and active cationic species present as a high spin quintet and the open-shell unpaired 3d-electrons reside on Fe center. The trans and cis polymerization of isoprene catalyzed by the complexes [(octyl-iminopyridine)FeII(Me)]+ (A1) and [(supermesityl-iminopyridine)FeII(Me)]+ (A2) could be attributed to the electronic and steric effects in the transition states, respectively.

Electron Configuration Modulation of Nickel Single Atoms for Elevated Photocatalytic Hydrogen Evolution.

The emerging metal single-atom catalyst has aroused extensive attention in multiple fields, such as clean energy, environmental protection, and biomedicine. Unfortunately, though it has been shown to be highly active, the origins of the activity of the single-atom sites remain unrevealed to date owing to the lack of deep insight on electronic level. Now, partially oxidized Ni single-atom sites were constructed in polymeric carbon nitride (CN), which elevates the photocatalytic performance by over 30-fold. The 3d orbital of the partially oxidized Ni single-atom sites is filled with unpaired d-electrons, which are ready to be excited under irradiation. Such an electron configuration results in elevated light response, conductivity, charge separation, and mobility of the photocatalyst concurrently, thus largely augmenting the photocatalytic performance.

Dehydration-triggered electronic structure modulation enables high-performance quasi-solid-state Li-ion capacitors

Ti-based oxides have attracted extensive attention as promising lithium-intercalated materials for hybrid capacitors. However, the low electronic conductivity and sluggish lithiation dynamics hinder their performance including reversible capacity, rate capability, and cycle stability. Herein, we report a kind of quasi-layered titanate hydrates (Q-TH) deriving from the dehydration-induced structural rearrangement of Ti-O octahedra and their superior electrochemical performance in the quasi-solid-state Li-ion capacitors. As predicted by Mulliken charge analysis, the surrounding O atoms will transfer electrons to the central Ti atoms accompanying with the detachment of bonding -OH groups. The resulting unpaired 3d electron would be injected into the t2g* antibonding orbital, deflecting the conduction band to the Fermi level and introducing intermediate bands within the bandgap, thereby enhancing the electronic conductivity of Q-TH. Such a special electronic structure will reduce polarization, facilitate fast Li-ion diffusion and lower the activation barrier (0.309 eV). Hence, impressive energy densities (116 Wh kg−1) and competitive cycling ability (86%, 3000 cycles) can be achieved when used as additive-free anodes in quasi-solid-state LICs with graphene nanosheets (GNS) cathodes. Thus, dehydration could be an effective way to modulate the electronic structure of titanate hydrates instead of just an approach to removing water.

Unpaired 3d Electrons on Atomically Dispersed Cobalt Centres in Coordination Polymers Regulate both Oxygen Reduction Reaction (ORR) Activity and Selectivity for Use in Zinc-Air Batteries.

Reversible oxygen conversion is important for various green energy technologies. Herein we synthesize a series of bimetallic coordination polymers by varying the Ni/Co ratio and using HITP (HITP=2,3,6,7,10,11-hexaiminotriphenylene) as the ligand, to interrogate the role of metal centres in modulating the activity of the oxygen reduction reaction (ORR). Co3 HITP2 and Ni3 HITP2 are compared. Unpaired 3d electrons in Co3 HITP2 result in less coplanarity but more radical character. Thus, despite of a reduced crystallinity and conductivity, the best ORR activity, comparable to 20 % Pt/C, is obtained for Co3 HITP2 , showing the 3d orbital configuration of the metal centre promotes ORR. Experimental and DFT studies show a transition of ORR pathway from four-electron for Co3 HITP2 to two-electron for Ni3 HITP2 . Rechargeable zinc-air batteries using Co3 HITP2 as the air cathode catalyst demonstrate excellent energy efficiency and stability.

Unpaired 3d Electrons on Atomically Dispersed Cobalt Centres in Coordination Polymers Regulate both Oxygen Reduction Reaction (ORR) Activity and Selectivity for Use in Zinc–Air Batteries

AbstractReversible oxygen conversion is important for various green energy technologies. Herein we synthesize a series of bimetallic coordination polymers by varying the Ni/Co ratio and using HITP (HITP=2,3,6,7,10,11‐hexaiminotriphenylene) as the ligand, to interrogate the role of metal centres in modulating the activity of the oxygen reduction reaction (ORR). Co3HITP2 and Ni3HITP2 are compared. Unpaired 3d electrons in Co3HITP2 result in less coplanarity but more radical character. Thus, despite of a reduced crystallinity and conductivity, the best ORR activity, comparable to 20 % Pt/C, is obtained for Co3HITP2, showing the 3d orbital configuration of the metal centre promotes ORR. Experimental and DFT studies show a transition of ORR pathway from four‐electron for Co3HITP2 to two‐electron for Ni3HITP2. Rechargeable zinc–air batteries using Co3HITP2 as the air cathode catalyst demonstrate excellent energy efficiency and stability.

Tuning room temperature ferromagnetism of ‘in-situ’ inkjet printed Fe-doped ZnO films

ZnO is a wide-band gap semiconductor widely used in optical and electric devices, associating with ferromagnetism at low dimension endowing its possibility for functional applications with magneto-optical and magneto-electric properties. We prepared ZnO and Fe-doped ZnO thin films ‘in-situ’ on substrate by inkjet printing, and tuned the room temperature ferromagnetism (RTFM) of the film by Fe-doping concentration, film thickness and post annealing temperature. It was found that by Fe doping the saturation magnetization (MS) of the film can be enhanced by more than 4 folds comparing with the un-doped film, i.e. from 0.9 emu g−1 for the ZnO film to 3.8 emu g−1 for the Fe-doped ZnO film with comparable thickness. The enhancement was attributed to the introduction of un-paired 3d electrons which formed long range ferromagnetic ordering, as well as the consequent structure changes with smaller grains which increased the interface induced magnetism. By changing the annealing temperature and the film thickness, the defect-induced ferromagnetism was investigated. The RTFM shows thickness dependence with peak saturation magnetization value of 4.44 emu g−1 for the 45 nm thick film. The work provides an effective way of tuning magnetism in ZnO based films for functional device applications.

Modulating the electronic and magnetic properties of the marcasite FeS2 via transition metal atoms doping

First-principles calculations are used to investigate the electronic and magnetic properties of substitutional doping of transition metal (TM) atoms (V, Cr, Mn, Co, Ni, Cu and Zn) on marcasite FeS2 (m-FeS2). It is energetically favorable to combine TM atoms into m-FeS2 under S-rich condition. The electronic properties of m-FeS2 are changed significantly due to the introduced impurity states by TM atoms. Simultaneously, TM atoms doping can induce magnetism in m-FeS2 except Cu and Zn. The magnetism stem from the localized unpaired 3d electrons of TM atoms, a small amount of magnetic moments are induced in the neighboring Fe and S atoms due to the p–d hybridization mechanism. V-, Mn- and Ni-doped m-FeS2 compounds exhibit magnetic semiconducting character, Cr-doped compound display a half-metallic property, while Cu-doped compound shows non-magnetic metallic property, Zn-doped compound behavior as a non-magnetic semiconductor. More interestingly, a single Co-doped compound shows magnetic semiconducting but double Co-doped compound shows half metallic character. In addition, Co- and Cr-doped compounds prefer ferromagnetic state which is important for spintronics.